1. Field of the Invention
The present invention relates to a gasifying combustion method for gasifying crude fuel such as heavy oil, coal and the like so as to be able to use it as working fuel in a combined cycle making use of, for instance, a gas turbine, and also relates to a gasifying power generation method.
2. Description of the Prior Art
FIG. 4 is a system diagram showing one example of an apparatus for practicing a gasifying combustion method in the prior art.
With reference to this figure, at first coal 310 and desulfurizing agent 311 are fed to a fluidized bed gasification furnace 301. In this fluidized bed gasification furnace 301, coal 310 is gasified, and a sulfur component in the coal is fixed by the desulfurizing agent 311 as calcium sulfide (CaS). Combustible gas 313a produced by gasification of the coal 310 is dedusted in a dust removing device 303a. Combustible gas 313b after dedusting is introduced to a secondary combustor 305.
On the other hand, a mixture 315a of char produced from the coal not gasified in the fluidized bed gasification furnace 301 and the desulfurizing agent, and a mixture 315b of char and the desulfurizing agent collected in the dust removing device 303a, are fed to a fluidized bed combustion furnace 302. To this fluidized bed combustion furnace 302 is also fed air 312b, and a combustion reaction of char and a reaction of calcium sulfide being oxidized and transformed into gypsum (CaSO.sub.4) arise. In addition, within the fluidized bed of the fluidized bed combustion furnace 302 is installed a heat exchanger 307 and a fluidized bed temperature is regulated by cooling with steam or water 318.
Combustion gas 314a produced in the fluidized bed combustion furnace 302 is dedusted by a dust removing device 303b. Combustion gas 314b after dedusting is introduced to the above-mentioned secondary combustor 305. In the secondary combustor 305, the combustible gas 313b produced in the fluidized bed gasification furnace 301 is burnt by residual oxygen in the combustion gas 314b introduced from the fluidized bed combustion furnace 302 and separately fed air 312c, and produced combustion gas 317 is sent to, for example, a gas turbine (not shown).
An ash component in the coal 310 and the desulfurizing agent 311 after desulfurization are removed as extraction ash 316a from the bottom of the fluidized bed combustion furnace 302, and as exhaust ash 316b from the dust removing device 303b, respectively, and discharged to the outside of the system.
In the case where it is intended to increase the amount of the combustion gas 317, the amounts of coal 310 and the air 312a fed to the fluidized bed gasification furnace 301 are increased. Then, the char and the desulfurizing agent 315a sent from the fluidized bed gasification furnace 301 to the fluidized bed combustion furnace 302, would increase. Hence, according to the increased amount of the char entering the fluidized bed combustion furnace 302, the feed amount of the air 312b is increased. In the case where it is intended to decrease the amount of the combustion gas 317, the gas 310 and the air 312a fed to the fluidized bed gasification furnace 301 are decreased, and thereafter, according to the decreased amount of the char entering the fluidized bed combustion furnace 302, the feed amount of the air 312b is decreased.
Next, one example of an electric power generation method making use of heavy oil in the prior art will be described with reference to FIG. 5.
Heavy oil 601 is pressurized by a pressurizing pump 502 and then fed to a gasification furnace 525. In the gasification furnace 525, a part of the fuel 601 is burnt with pressurized air 607, and carbon is gasified and transformed into gaseous fuel by making use of the combustion as a heat source. Combustible gas 608 produced in the gasification furnace 525 is cooled to 350.degree. C.-450.degree. C. by heat-exchange with water 610 in a heat-exchanger 524. The combustible gas 608 after cooling is subjected to dedusting treatment in a porous filter 505, becomes a gas having a dust concentration of about 1 mg/Nm.sup.3 or less, and it is sent to a desulfurizing device 526 in which H.sub.2 S in the combustible gas 608 is removed by making use of desulfurizing agent of the iron oxide group. Combustible gas 608a after dedusting and desulfurization is fed to a combustor 507, then it is burnt with pressurized air 607c and becomes combustion gas 609, its temperature is held at 1150.degree. C.-1300.degree. C., and it is fed to a gas turbine 509 to drive the same gas turbine 509.
The pressure of the combustion gas 609 fed to the gas turbine 509 is determined so that a sending end efficiency of the power generation system may become maximum once the temperature of the combustion gas 609 is determined. Energy of the combustion gas 609 is given to the gas turbine 509, and electric power generation is effected by driving a generator 517 with that energy. Combustion gas 609a at the outlet of the gas turbine 609 has its heat transmitted to water 610 in an exhaust gas boiler 510, and after its temperature has lowered to 120.degree. C.-130.degree. C., it is exhausted to the atmosphere through a stack 514.
Within the above-mentioned exhaust gas boiler 510 is provided a heat-exchanger 521 to which water 610 having cooled the combustible gas 608 is introduced, and in the exhaust, gas boiler 510, thermal energy is transmitted from the abovementioned combustion gas 609a to the water 610 having been heated by the combustible gas 608 in the heat-exchanger 524, and the water 610 is transformed into steam 611. Energy of the steam 611 is given to a steam turbine 511, and electric power generation is effected by driving a generator 518 with that energy.
Unburnt carbon and an ash component produced within the gasification furnace 525 are exhausted from the gasification furnace 525 through a piping 612 and hoppers 515c and 516c to the outside of the system as exhaust ash 605a. In addition, soot and dust collected from the combustible gas 608 by means of the porous filter 505 are exhausted through a piping 617 and hoppers 515d and 516d to the outside of the system as exhaust ash 605b.
In addition, reference numeral 508 designates a compressor directly connected to the gas turbine 509, and the compressor 508 is adapted to pressurize intake air 603 and feed the pressurized intake air 607c to the combustor 507 and feed the pressurized air 607 to the above-mentioned gasification furnace 525.
However, in the known gasifying combustion method in the prior art illustrated in FIG. 4, the heat-exchanger 307 for controlling a combustion temperature is installed in the fluidized bed combustion furnace 302. Accordingly, a part of the energy of the fuel is collected directly by a steam turbine without being sent to the gas turbine in the form of sensible heat of the combustion gas, and so, there was a problem that a power generation efficiency is lowered by the amount corresponding to the sensible heat which wont't be used by the gas turbine.
Also, in this known method in the prior art, as the amount of the air 312b in the fluidized bed combustion furnace 302 is regulated according to an increase or decrease of the exhaust char from the fluidized bed gasification furnace 301, the speed in which the amount of the combustion gas 317 can be varied is slow.
Furthermore, since variations in the amount of transfer of char between the fluidized bed gasification furnace 301 and the fluidized bed combustion bed 302 is regulated by a distributing ratio of a fixed amount of air 312 between the fluidized bed gasification furnace and the fluidized bed combustion furnace 302 in order to maintain the temperature of the combustion gas 317 at a constant value, there was a shortcoming in that in varying the amount of the combustion gas 317, the respective reactors (furnaces) would become very complicated to control.
In addition, in the power generation method in the prior art illustrated in FIG. 5, since iron oxides were employed as the desulfurizing agent to be used in the desulfurizing device, the desulfurizing temperature was most preferably 400.degree. C.-450.degree. C. To that end, it was necessary to cool the combustible gas produced in the gasification furnace to 400.degree. C.-450.degree. C. Because of the fact that it was necessary to cool the combustible gas at the outlet of the gasification furnace to 400.degree. C.-450.degree. C. as described above, a part of the thermal energy of the combustible gas produced in the gasification furnace is not used as energy for driving a gas turbine but is used to heat the steam for driving a steam turbine. Thus, the power generation efficiency of the prior art combined electric power generation plant, in which a gas turbine and a steam turbine are used in combination, cannot, theoretically, be made maximum.